Insect resistance of chlorpyrifos-methyl and permethrin-treated film overwraps on cases of packaged food

Paperboard shipping cases containing individual meals in plastic pouches were wrapped in polymer films treated with permethrin or chlorpyrifos-methyl. Because chlorpyrifos-methyl killed all insects in the test room, separate rooms had to be used for the two treated films. Permethrin-treated film, while not toxic to Tribolium castaneum (Herbst) in bioassays, prevented damage to the plastic pouches for 30 months, and no live insects were found in these cases. Chlorpyrifos-methyl-treated film remained toxic to T. castaneum for < 15 weeks in bioassays. Adjacent untreated film wraps and surfaces of untreated cases were toxic for < 11 weeks because of translocation of chlorpyrifos-methyl. At 24 months 18.1% of the original chlorpyrifos-methyl treatment was found in the film and cases, while at the same time 62.1% of the original permethrin treatment was found in the film.